Evaluation of tissues collected from dairy cattle in a barn recently constructed with pentachlorophenol treated lumber detected the presence of various chlorinated dibenzodioxins. The presence of these contaminants of pentachlorophenol in animal tissues suggests that studies be undertaken that define the circumstances associated with body accumulation of these contaminants as a consequence of exposure to pentachlorophenol. Attempts should be made to simultaneously correlate any adverse health effects that may be associated with body burdens of these chemical contaminants.